This invention relates generally to non destructive testing, and in particular, to a computerized system for eddy current testing using the phase and amplitude change in output signals for crack detection.
In the broad field of materials testing, be it non destructive or not, there is a constant effort to improve methods to achieve more accurate test results. Further, objects of improvements in this field aim toward providing methods and means for simplification of the testing process while maintaining a high degree of reliability in the test results.
One of the most important areas of non destructive testing resides in the aircraft industry. Aircraft, because of the high safety requirements, are tested regularly for metal fatigue and unusual or unexpected wear. In the case of fastener holes, it is common and practical to utilize inspection equipment operating on the eddy current principal. These detection devices have proven their value except in the situation where the inspection process does not call for a removal of the installed fastener. An example would be where a wing-splice occurs, and perhaps two layers of wing material are held in place by a titanium or steel fastener. Cracks developing under these fasteners cannot be detected with the convenience of an eddy current detection system without removal of the fastener. One of the reasons for this is that, to observe such discontinuities, the eddy-current detector must function at a relatively low frequency and all known detectors show much instability at these low frequencies. The convenience is lost in the lack of reliability of the instrument.
We have developed a new and improved eddy current detection system that is highly stable and reliable and will provide the convenience of the eddy current detector of the inspection for cracks under installed fasteners and other like devices.